Electric power steering (EPS) has long been the subject of development by automobile manufacturers because of its fuel economy and ease-of-control advantages as compared to the traditional hydraulic power steering (HPS). However, commercialization of EPS systems has been slow in coming and is presently limited to smaller automobiles due to the cost and performance challenges associated with larger automobiles. Among the challenging technical issues addressed is the use of a sensor positioned on a steering shaft coupled to a steering device and the effect of dirt build-up on the sensor. Dirt build-up typically distorts sensed information associated with the type of high performance sensors needed to meet the steering requirements.
At least two methods for the sensing the rotary positioning of a steering shaft exist. One method utilizes semiconductor-based magnetic sensors (magnetoresistors, or MRs). A second method utilizes the sensing of a signal based on optical detection and magnetic field variation. In the second method, the functionality of optical detectors and encoders is dependent upon environmental and operating conditions. Such conditions typically include dirt build-up and temperature variations, which increase the probability of the occurrence of distortion in the sensed signal.